Technical Field
The present invention relates to an oil-retaining sintered bearing in which smooth lubrication can be performed by impregnating lubricant oil therein and a producing method thereof.
Background Art
An oil-retaining sintered bearing is used in a state in which pores are impregnated with lubricant oil. When a shaft is rotated, the lubricant oil is exuded from the bearing between the shaft and a sliding surface of the bearing so as to support the shaft by pressure of the lubricant oil generated along with the rotation of the shaft. The oil-retaining sintered bearing is broadly used as a bearing for an in-vehicle motor and the like because it can be used for long time without oiling by such a lubrication property.
In this oil-retaining sintered bearing, in order to appropriately generate the pressure of the lubricant oil on the sliding surface, a means to reduce a leak of the lubricant oil from the sliding surface and the like are applied by increasing a passage resistance of the lubricant oil by sealing a part of the pores or reducing sizes of the pores in the bearing.
For example, Japanese Unexamined Publication No. H04-307111 discloses a method of producing an oil-retaining sintered bearing by forming a pressurized powder body and then sintering it: when the pressurized powder body is formed, a penetrated hole to be a bearing hole is formed by using a rod: the rod has a roughened part with a surface roughness larger than that of the other part on a part of an outer peripheral surface; the roughened part is formed along a shaft direction: so that the pores at an inner peripheral surface of the penetrated hole which are in contact with the roughened part are crushed. In this oil-retaining sintered bearing, the shaft is held at a part of the inner peripheral surface in which the pores are crushed in the bearing hole: oil is exuded from the other part than the part in which the pores are crushed of the inner peripheral surface, and supplied to the inner peripheral surface at which the pores are crushed.
In this case, the roughened part is formed in a belt shape along the shaft direction of the rod: accordingly, a part around the pores are pressed by the roughened part of the rod when the powder is pressurized and formed, and they plastically flow into the pores and are crushed. Moreover, it is described that a part in contact with the roughened part is formed to be slightly protruded, and flattened with the inner peripheral surface of the bearing hole by being pressurized by sizing.
Japanese Unexamined Publication No. H05-115146 discloses an oil-retaining sintered bearing in which step parts to be sliding surfaces are formed on an inner peripheral surface of a bearing hole along a circumferential direction so that spaces are formed between bottom surfaces of groove parts between the step parts adjacent to each other and a shaft; and aeration at the sliding surfaces of the step parts is smaller than aeration at the inner peripheral surface of the bearing hole. In this case, the aeration at the sliding surfaces of the step parts is set to be 3×10−10 cm2, the aeration at the bottom surfaces of the groove parts is set to be 30×10−10 cm2, and height of the step parts is set to be 0.02 mm. As means to reduce the aeration at the sliding surfaces of the step parts, sealing by filling up, plating, or coating are exemplified. It is described that, in this oil-retaining sintered bearing, the shaft is in contact with the sliding surfaces of the step parts but is not in contact with the bottom surfaces of the groove parts having the larger aeration, so that a prescribed amount of oil can be drawn and discharged at the groove parts, and dynamic pressure can be generated in a space surrounded by the groove parts and the shaft.
Technical Problem
Japanese Unexamined Publication No. H04-307111 does not specifically describe aeration at the surface formed by the roughened part or the other surfaces. If the aeration is in a degree described in Japanese Unexamined Publication No. H05-115146, it is difficult to reduce the leakage of the oil from the sliding surfaces while supplying sufficient oil as a bearing in operation in a high-speed rotation or the like, seizing and the like may be generated.
The present invention is achieved in consideration of the above circumstances, and has an object to improve sliding property as a bearing by reducing friction coefficient, by supplying sufficient amount of oil to a sliding surface and preventing the supplied oil from moving inside from the sliding surface.